1. Field of the Invention
The present invention relates to an image capturing apparatus and an electronic zoom method which can be applied to a digital camera having an electronic zoom function.
2. Description of the Related Art
Conventionally, an image capturing apparatus having an electronic zoom function such as a digital camera is provided with the following technique for acquiring a partial image of an area corresponding to a zoom magnification. In order to read out an image signal from an image sensor, such as a charge coupled device (CCD), a pixel-thinning mode and pixel-addition modes are prepared as a reading mode in addition to a normal reading mode. In the pixel-addition modes, the number of pixels utilized for pixel-addition is varied. The image signal including the number of pixels (pixel size) corresponding to the zoom magnification is acquired by switching the reading modes depending on the electronic zoom magnification. A partial image of a preset area is extracted from an image based on the acquired image signal. Then the extracted image is scaled. The technique for acquiring a partial image of an area corresponding to the setting of the zoom magnification is described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-172845, Jpn. Pat. Appln. KOKAI Publication No. 2005-191867, Jpn. Pat. Appln. KOKAI Publication No. 2004-72278, Jpn. Pat. Appln. KOKAI Publication No. 2004-96611.
However, at the time of switching the reading modes, the image quality changes discontinuously. The change in the image quality is caused by factors such as a variation in the number of pixels utilized for the pixel-addition, a variation in the pixel-thinning rate or a variation in the enlargement or reduction ratio. Therefore, the image quality after the extraction and the scaling processes is greatly changed at the zoom magnification where the reading mode is switched.